Loud Valve Single Knock

[Malcolm99]

Hey everyone, long time 4R owner and wrencher, this is my 3rd 4R over the past 15 years and I come from the DSM modified world so I'm use to working on the Japan stuff and consider myself knowledgable, but this has me confused.

1999 Limited 5vz-Fe Automatic 290,000Km(CAD) MFG date: Nov 98, VZN185L-GKPZKA A04A/A340F. The issue, at idle 700-750RPM once it is warmed up, if I "blip" the throttle aggressively in neutral I get a loud single Knock/clack sound metal on metal in the valve train on cylinder number 6(last cylinder on the fuel rail*), it will also do this in gear under the same conditions, I never really noticed it until I did the deck plate mod years ago(a worthless mod not used) which either exaggerated the noise or induces more preignition or both, it has always done this since I noticed it after doing the deck plate mod only under these exact conditions, with the deck plate closed it is difficult to hear in the cab and sounds like preignition knock if you had the window down, never heard when driving under any other condition or load that I noticed. I got the truck @ 140,000Km/9 years ago, no power loss that I've noticed between my other 4R's, I think it is preignition, it is easily repeated by operating the throttle plate under these exact conditions and a pretty loud single knock/clack when your head is under the hood. I did the valve covers awhile ago but didn't check valve clearance unfortunately. I think it might be low fuel pressure as I have had some of the common 5vz-fe extended cranking on start up since I got it. can anyone reproduce this single knock on their 4R under these exact conditions?. I ordered a fuel pressure tester to see if I can see a drop in fuel pressure under these conditions, I'm sure the check valve on the pump is draining back into the fuel tank contributing to the extended crank- 5 revolutions approx. My main concern is the loud knock, revs smoothly, runs smooth, but doesn't like the throttle blip from 700RPMs or you get a brief single clack, cannot reproduce this on my other 1997 4R with 500,000Km. With a stethoscope I can isolate the noise to be coming from the valve cover and obviously #6, not the block. Maybe I shouldn't blip the throttle like that but I do enjoy a little wheel spin every now and then on the dirt roads and blip the throttle to get over obstacles, but I might be lugging the motor doing this, normal steady throttle operation, or even blipping the throttle when RPMs are above 800 eliminates the single knock sound.

This is what I've done so far to eliminate possibilities.
No code or pending codes even after reproducing this Knock
Denso Toyota plugs, the NGK's looked prefect, light brown after 100,000Km so bit lean*
Sumitomo Wires
Swapped all 3 working tested coils from another 4R
Compression test 190-195(EFI pulled, WOT 3-4 revolutions approx)
looked in cylinders with camera, pretty clean with usual thin layer of carbon.
Fogged cylinders with engine storage oil
Cleaned throttle body
Valve covers gaskets (looked very clean inside)
new PCV
Replaced intake gaskets.
Thermostat replaced, runs at 190-193*
Intake leak test
Cleaned MAF
Check TPS range 10-74, disconnect TPS vacuum idle raises as it should.
Starter contacts replaced(cranks faster now)
OEM fuel filter and main fuel supply line from filter to engine(original seized on)
SGII LTFT seems to be at +19 under acceleration*, +14 cruising flats
STFT hovers between -6 & +6 load dependant, both close to 0 at idle
tried premium gas and additives
Fuel gauge, filler neck and Cluster inclinometer TSB completed at Toyota 8 years ago
Checked crank bolt was tight, Have to add 250FTLB TW to the list,
Harmonic balancer runs true and straight
Castrol 5w30 Synthetic since I got it, OEM D3 bigger oil filter.
Oil seems metal free every 10,000Km but i have never cut open a filter.
No oil loss over 10,000Km NONE, no radiator fluid lost.
Shot a timing light on it and everything checks out.
Lexus did the Timing belt at 140,000Km, I assume its correct since the PO's husband was a Lexus salesman where all its servicing was done, although I should never assume so I'll check that while I wait for the fuel pressure tester and report back if I find anything out of the norm.

 

[gamefreakgc]

The most common cause of a valve tap is a valve that's out of adjustment. Unfortunately the only way to check the valve clearances is to pull the valve covers which is a little bit of work. The acceptable gaps between the shims and the lobe on the camshafts are printed on a sticker on the hood. Over time, the exhaust valves tend to expand and the clearance will shrink or eliminate altogether, causing poor compression and noise. Intake valves go out of spec less often.

If you have a compression tester on hand, test the compression on the bank of the engine with the knock, so it sounds like that will be 2, 4 and 6. That will give you a clue if the valves are out of adjustment since you will see a noticeable compression loss in one of those cylinders. I do recommend checking all valve clearances on that head though as if one is out of spec, others probably are but just aren't giving you the symptoms of valve knock and compression loss. Toyota uses a shim-over-bucket design to adjust the valves you'll need to remove the offending shim, measure it with a caliper and take it to your Toyota dealership. You'll want to increase or decrease the clearance by inserting a thicker or thinner shim.

There's lots of videos on Youtube and writeups on here that go into more detail.

 

[Malcolm99]

Compression was 190-195 on all cylinders, 195 on offending cylinder, exactly the same as when I bought the truck.
Yes, I'm familiar with the valve check and adjustment procedure, but skipped it as I would have had to order the unknown shims and be down a few days and at the time I was still thinking preignition, I've also never bothered to check the valves on my other 2 high mileage motors and all 3 ran like a top and still do, but I realize it should be done every 100,000km according to the FSM, but I see no compression loss, no spark plug variance between cylinders, and no valve noise/clatter/ticking just a single Knock under these exact conditions, which is why I'm leaning(no pun intended towards weak fuel pressure, maybe even a voltage drop in that circuit causing a pressure drop on the last injector on the rail, no misfires I should add, runs smoothly as mentioned. On that note I should mention the battery is 1 year old as is the alternator, all connections and grounds are clean and in place.